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The recent failure of the Hitomi satellite to find X-rays from black holes and galaxy clusters represents a devastating fiasco in the history of space science and has caused great disappointment to X-ray astronomers around the world, since the satellite was regarded as a flagship satellite for their research. The Japan Aerospace Exploration Agency (JAXA) needs to do its utmost to find out what went wrong with the project and learn lessons so that such failures are not repeated.

The Hitomi X-ray astronomy satellite was launched on Feb. 17 aboard Japan’s mainstay H-IIA rocket from the Tanegashima Space Center in Kagoshima Prefecture. But it started spinning while in orbit around the Earth and communication with it was lost on March 26, bringing the operation of the satellite during its trial observation to a virtual halt on the 39th days of its mission. JAXA officially abandoned the project on April 28. The satellite had been scheduled to start full-scale observations this month.

The satellite was developed jointly by JAXA, NASA and other concerns. Some 250 researchers from Japan and abroad took part in the project, in which JAXA poured ¥31 billion, including the launch cost.

A satellite is indispensable to observe X- and gamma rays coming from celestial bodies because such rays are absorbed by the Earth’s atmosphere and it is impossible to detect them with instruments on the surface of the planet. The satellite, which was formerly called Astro-H, was renamed Hitomi, or eye pupil in Japanese, in the expectation that it would serve as an eye to watch hot outer space.

Equipped with four X-ray telescopes that were over 10 times more powerful than conventional types and two gamma-ray detectors, and orbiting about 580 km above the Earth’s surface, the satellite was designed to observe high-temperature, high-energy celestial bodies such as black holes — believed to be huge collapsed stars whose enormous gravitational pull is so strong that nothing can escape — and supernovas — large explosions that take place at the end of a star’s life cycle. Through these observations, the researchers hoped to find clues about dark matter — a hypothetical type of matter composing about 27 percent of the mass and energy in the observable universe — and dark energy — an unknown form of energy hypothesized to permeate all of space, tending to accelerate the expansion of the universe.

About a week before the launch of the Hitomi in February, the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced that its twin detectors located in the United States had detected gravitational waves last September — the first observation of gravitational waves, whose existence Albert Einstein predicted 100 years ago on the basis of his theory of general relativity. LIGO thinks that the detected gravitational waves were produced through a merger of two black holes, 29 and 36 times the mass of our sun, which took place 1.3 billion years ago and that about three times the solar mass were converted into gravitational waves. It was hoped that the Hitomi would search for a merger of black holes, a source of gravitational waves, which are ripples produced by accelerating masses that propagate gravitational energy across the universe. Expectations were high for the Hitomi mission since there will be no launch of a similar satellite until 2028, when the European Space Agency is to start a new mission.

According to JAXA’s analysis of the Hitomi mishap, the satellite’s computer misjudged on March 26 — while preparations were being made for full-scale observations — that the satellite was rotating though in fact it was not. This led an apparatus that controls the satellite’s attitude by using inertia to kick in and the satellite’s small engines to start emitting jets. As a result, the satellite began to spin at a high speed, causing its six solar panels, three on each side, that provide power for the precision instruments to come adrift due to centrifugal force and break into more than 10 fragments. Such a setback is unprecedented in the history of the launch and operation of artificial satellites. JAXA thinks that the computer’s software had problems. The accident should serve as a heavy lesson for future space projects.

The Hitomi, 14 meters long and weighing 2.7 tons, was the largest satellite Japan has ever built and launched. It is imperative that JAXA examine whether the attitude control system was adequate to handle this heavy satellite. Although its budget is limited, the agency needs to strengthen self-rectification functions of its satellites. JAXA must also find out whether tests in the development stage and instructions to the satellite after the launch were appropriate.

The organization should also develop a system that will enable communications between a satellite and the ground command team even when the power supply from the solar panels to the satellite’s communications system is cut off. It needs to design a satellite that has the ability to prevent itself from falling into the worst situation even if it experiences some problems. Utilizing cheap, multi-use small satellites, instead of focusing on big and heavy satellites alone, could be worth trying.

Japan’s space science has made accomplishments in the operations of the asteroid exploration satellite Hayabusa and the Venus observation satellite Akatsuki. Although Japan was once reputed to be good at operating X-ray astronomy satellites, it failed in the launch of the Astro-E in 2000 and main equipment of the Suzaku ran into trouble after its launch in 2005.

The abandoning of the Hitomi represents the third straight failure in the operation of X-ray astronomy satellites. In space science, both successes and failures stand out. It should be JAXA’s duty to do everything it can to regain the position it held in the field of X-ray astronomy through the efforts over the past four decades.

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